Keep a light grip on the pick so it can flex in your finger. Use only your thumb and index finger to hold the pick.
Lastly, your down strums should strike all of the strings relevant to the chord in a light, brushy motion. Your up strums should only strike 3 or 4 of those strings in a slightly lighter, brushy motion.
If you do those things and your strumming will sound great!
Earle Wood
www.ewguitar.com